This invention relates to systems and methods for synthesizing germanium selenide glass and germanium selenide glass compounds. More particularly, this invention relates to systems and methods for large scale synthesis of germanium selenide glass and germanium selenide glass compounds in reduced time.
As used herein, a germanium selenide glass compound includes germanium, selenium, and a variable (e.g., a dopant).
Germanium selenide glass is widely used in the fabrication of semiconductor devices. However, in a known technique for producing Ge3Se7, which is one type of germanium selenide glass, only about ten grams of that glass can be produced at one time. Moreover, this technique requires about 50 hours in order to produce those ten grams of germanium selenide glass.
The known technique involves placing stoichiometric proportions of germanium and selenium (totaling no more than about ten grams) in an ampoule at atmospheric pressure (i.e., at about 1 atm.). An ampoule is a small, hermetically sealed quartz-glass vessel that is typically used to hold chemical solutions or materials. A vacuum is established in the ampoule, which is then flame sealed to seal the contents under vacuum. The ampoule is placed in a furnace and heated to about 300° C. and typically left at this temperature overnight. The next morning, the ampoule is heated to about 750° C. at a rate of about 0.5° C./minute. The ampoule is left at this temperature until the following morning to ensure that the germanium has melted and that the selenium has reacted with the germanium. If the melting and reaction do not occur, the selenium can exhibit a vapor pressure of about 10 atm. at about 900° C., which may burst the ampoule. The following morning, the temperature of the ampoule is increased to about 940° C. at a rate of about 0.5° C./minute. This ensures that the contents of the ampoule have melted. Once the temperature reaches about 940° C., the ampoule is rocked back and forth (typically by a rocking mechanism connected to the furnace) for at least about six hours. During rocking, the ampoule is allowed to cool down to a range of about 800° C. to about 780° C. After the ampoule has cooled down, it is quenched in a cooling bath of ice water. The ampoule is then cracked to retrieve the germanium selenide glass.
The only known way to scale-up the synthesis of this germanium selenide glass using this known technique is to run multiple small scale reactions concurrently, in which each reaction produces only about ten grams of glass per 50 hours. Clearly, this technique is very time consuming and impractical for large scale production.
Germanium selenide glass is particularly used in the fabrication of semiconductor devices, such as, for example, PCRAM (programmable cell random access memory). In the fabrication of known PCRAM devices, a thin layer of a conductive material (e.g., silver) is deposited over a germanium selenide glass substrate. The conductive material is typically irradiated with electromagnetic energy resulting in a doped or photodoped substrate (i.e., a germanium selenide glass compound). If care is not taken while irradiating the conductive material, such an irradiation may unpredictably change the properties of the substrate as well as result in an unpredictable amount of doping. Such changes or unpredictable amounts of doping may unpredictably, and usually undesirably, alter the electrical and performance characteristics of the PCRAM device being fabricated.
Moreover, similar to the synthesis of germanium glass, there is no known technique for synthesizing germanium selenide glass compounds on a large scale.
In view of the foregoing, it would be desirable to be able to synthesize more than ten grams of a germanium selenide glass or a germanium selenide glass compound in one reaction.
It would also be desirable to be able to synthesize a germanium selenide glass or a germanium selenide glass compound in one reaction in less than about 50 hours.
It would further be desirable to be able to synthesize a germanium selenide glass compound having substantially known properties and a substantially known amount of doping.